Impact roller apparatus

ABSTRACT

The invention provides an impact roller in which its crosssectional profile is deformable to permit variation of the lift of the centre of gravity of the roller. Thereby the impact delivered by the roller to underlying soils and gravels may be varied.

United States Patent 1191 1111 3,788,757 Berrange Jan. 29, 1974 [54] IMPACT ROLLER APPARATUS 2,909,106 10/1959 Berrange 94/50 PR X 3,114,305 12/1963 Davis..... 94/50 PR [75] Inventor: Aubre Ralph BYOOklYn, 3,080,799 3/1963 Calfee 94/50 PR Pretorla, South Afrlca 3,252,389 5/1966 Gardner 94/50 P x 73 2,674,165 4/1954 Paramythioti... 94/48 1 Asslgnee Pretoria 2,704,968 3/1955 Paramythioti.... 94/50 R 3,108,519 10/1963 Domenighetti 94/50 V South Afnca [22] Filed: Jan. 27, 1971 Primary ExaminerNi1e C. Byers, Jr. 1211 Appl' l10l47 Attorney, Agent, or Firml(arl W. Flocks [30] Foreign Application Priority Data Feb. 5, 1970 South Africa 70813 [57] ABSTRACT [52] US. Cl. 404/124 [51] Int. Cl. E011: 19/26 The invention provides an impact roller in which its [,58] Field of Search 94/50 PR, 50, 50 V, 50 P; cross-sectional profile is deformable to permit varia- 404/122, 124, 121 tion of the lift of the centre of gravity of the roller.

Thereby the impact delivered by the roller to underly- [56] I References Cited ing soils and gravels may be varied.

UNITED STATES PATENTS 2,776,532 l/1957 Buchholz 94/50 PR X 5 Claims, 9 Drawing Figures Pmimiu z 3.788.757

INVENTOR AUBREY RAlPH BERRANGE 27 W A T TOANE Y PATENTEU 3, 788,757

sum 2 or 2 BACKGROUND OF THE INVENTION This invention relates to improvements in or relating to impact compaction of layers of soils and gravels. The invention relates in particular to an improved impact roller and to an improved method of impact compaction by employing an impact roller.

An impact roller is a roller having a non-circular crosssectional profile. When such a roller travels over a surface, rotation of the non-circular cross-sectional profile causes the centre of'gravity of the roller to rise and fall continuously, thereby delivering impact to the underlying material upon descent ofthe centre of gravity. The impact delivered depends on a number of factors, one important factor being the lift of the centre of gravity of the roller, i.e the vertical distance of travel of the centre of gravity between low and high positions.

The applicant has found thatwith impact rollers presently known to it, compaction is effected to a considerable depth below the surface. This depth is dependent on the geometry of the roller, the properties of the material operated on and the speed at which the roller is operated. With impact rollers presently known to the applicant. material in many instances is compacted to a much greater depth than required. This is obviously uneconomical and can only be rectified in the case of impact rollers presently known to the applicant. by a reduction in the speed of operation which is also uneconomical.

The applicant has also found that impact rollers as presently known to it, require a reasonably dense top layer of soil or gravel on which to operate. When such impact rollers are used, conventional equipment has to be employed from time to time to restore the top layer. This is also uneconomical as it involves either the tran sporation of conventional equipment from wherever it had been in use or to have the equipment standing idly by while impact rolling is in progress.

During construction work, impact rollers often have to cross structures such as culverts, bridges, buried sewerage pipes, water pipes and the like, which could easily be damaged or displaced by impact. Avoidance of such structures or services results in a waste of time, and nonuniform compaction standards because of the diffculty in manoeuvering the roller close to the structure. I

The applicant has also found that with impact rollers presently known to it, large varying forces are encountered in the drawbar at times when the roller is hauled at speeds substantially lower than the operating speed e.g. during acceleration and deceleration. This is un avoidably the case at the turning points of each run. To minimise these forces in such rollers, a combination of resilient and restraining means has to be used in a special arrangement to restrain excessive relative movement between the roller and the hauling vehicle.

It is an object of this invention to overcome or at least to minimise the above difficulties.

SUMMARY OF THE INVENTION According to the invention there is provided an impact roller in which its cross-sectional profile is deformable to permit variation of the lift of the centre of grav ity of the roller.

Further according to the invention there is provided a method of compacting layers of soils and gravels by means of an impact roller which includes varying the impact delivered by the roller by deforming its cross sectional profile to vary the lift of the centre of gravity of the roller.

The impact roller may conveniently have a plurality of adjustable curved lobes forming the periphery of the roller. Each lobe may be pivotally mounted on the roller and may extend on either side of the pivot.

Releasable locking means may be provided for locking each lobe in any desired position on the roller. The pivots of the lobes, and the locking means may be so arranged that the lobes are displaced and are reset in new positions by the rotation of the roller when the locking means is released.

The locking means may include a spring biassed clip' in arrangement. The clip-in arrangement may include a releasable catch adapted to engage any one of a plurality of notches, each notch effecting a particular lobe setting. Alternatively, the locking means may be operable by fluid pressure.

The curved lobes may be circular arcs and may be adjustable between one extreme position in which the cross-sectional profile of the roller is circular and no impact is delivered. i.e., the lift of the centre of gravity is zero, and another extreme position in. which maxi mum impact is-delivered, i.e., the lift of the centre of gravity is a maximum.

The depth and degree of compaction required in an underlying layer of soil or gravel is selected by selecting an appropriate lift for the centre of gravity of the roller. To achieve this, the cross-sectional profile of the 'roller is varied. When a low depth and degree of compaction is required the lobes are set so that the cross-sectional profile 'ofthe roller is only slightly non-circular and the lift is small. For a higher depth and degree of compaction the lobes are set so that the cross-sectional profile of the roller is more non-circular to obtain a greater lift.

When the surface to be compacted is too soft, rough or uneven, the surface may be prepared by first making a few passes with the roller so adjusted as to produce no lift, i.e., the roller has a circular cross-section. When the surface has been suitably prepared in this manner, the roller profile is adjusted to have a lift for the desired impact compaction.

When the surface operated on crosses structures which are vulnerable to impact such as culverts. bridges, sewerage pipes and the like, as is often found in urban areas. the roller could be adjusted to have a circular cross-section immediately prior to crossing such a structure. This would facilitate compaction to within close proximity to such structures.

The roller may be so arranged that its profile can be adjusted during operation without the necessity of having to stop the roller. This arrangement will permit an operator during operation-of the roller to adjust the profile of the roller either to deliver or not to deliver impact.

While the roller is hauled at speeds below the desired speed, i.e., during acceleration and deceleration, the roller profile may be adjusted to have a circular crosssection. When the desired operating speed has been reached, the roller profile may be restored to the original profile in which impact is delivered.

If desired, the roller may be self-propelled by imparting traction via the roller itself. An advantage of this arrangement is that it eliminates the drag caused between a hauled roller and the underlying soil by the soil tending to bank up in front of the roller when the roller is hauled. The roller may be driven by means of a motor mounted on the roller itself or on a trailing carriage.

The invention is now described by way of examples with reference to the accompanying drawings, in which:

FIG. 1 shows a side view of one embodiment of an impact roller having a deformable cross-sectional profile, the profile being adjusted to a circular shape;

' FIG. 2 shows the roller of FIG. 1 with its profile adjusted to a non-circular shape;

FIG. 3 shows a fragmentary view, partly in section, of

the roller shown in FIG. l but with an alternative pro file deforming arrangement;

FIG. 4 shows a side view of another embodiment of an impact roller similar to the roller shown in FIG. 1;

FIG. 5 shows a side view of another embodiment of an impact roller having a deformable cross-sectional profile, the view being partly fragmentary and showing a profile of a circular shape;

, FIG. 6 shows a sectional plan view on line V-V of FIG. 5;

FIG. 7 shows the roller of FIG. 5 with its profile deformed to a non-circular shape;

FIG. 8 shows a fragmentary side view of the roller shown in FIG. 5 but with slightly modified pivotal lobes; and

FIG. 9 shows a section on line IX IX of FIG. 8.

Referring to FIG. 1, reference numeral 10 indicates generally an impact roller having a core structure 12. On the core structure are mounted four curved lobes 14 whose external surfaces form the peripheral surface of the roller.

The drawing shows four lobes 14 but fewer or more lobes may be provided, if desired. Each lobe 14 is pivotally mounted on the core structure at 16 and has the curvature ofa circular arc. Each lobe 14 has a part 14.1 on one side ofthe pivot 16 and a part 14.2 on the other side of the pivot. The ends of each lobe are shaped to abut the ends of adjacent lobes when the lobes are adjusted to form a circular profile as shown in FIG. 1. In this geometry the centre of gravity 17 of the roller has no lift. i.e., it does not rise and fall during rolling ofthe roller over a surface- I Releasable locking means in the form of a hydraulic cylinder 13 and ram are provided for maintaining each lobe 14 in a locked position on the core structure 12. Each cylinder 13 is pivotally mounted on the core structure at 13.1 and each ram is pivotally attached to the lobe part 14.1 at 15.1. Alternatively, the locking means may be a spring-biassed clip-in arrangement (not shown).

Each hydraulic cylinder 13 and ram 15 in addition to hydraulically locking each lobe l 4 in a desired position, also pivots the lobe about its pivot 16 to vary the crosssectional profile of the roller. By means of a suitable hydraulic pump and valve arrangement (not shown) the rams 15 may be operated to pivot the lobes 14 while the roller 10 is in motion, ie. the roller profile may be adjusted while the roller is in operation.

The drawing shows four hydraulic cylinders 13 and rams 15, i.e.. one for each lobe 14 but if desired, only one or two such rams and'cylinders may be provided for operating all the lobes 14 simultaneously. Inthis arrangement the lobes 14 are interconnected by a lever 4 arrangement or a cam arrangement to permit operation by the rams provided.

FIG. 2 shows the lobes 14 adjusted to form a noncircular roller profile. With this profile the centre of gravity of the roller has a lift 19, i.e., R-r, and delivers impact to an underlying surface when travelling in the direction of arrow 18 to rotate in the direction ofarrow 20.

The profile of the roller is adjusted from that shown in FIG. 1 to that shown in FIG. 2 and vice versa by operating the rams l5, i.e., by varying the fluid pressure inthe cylinders 13, to pivot the lobes 14 about their pivots 16. When the lobes have assumed their new positions the rams 15 are hydraulically locked to maintain the lobes 14 in their new positions.

Alternatively, in order to adjust the roller 10 from the profile shown in FIG. 1 to the profile shown in FIG. 2, the locking means, i.e., hydraulic rams 15 are released while the roller continues to rotate in the direction of arrow 20. During rotation in this direction, the lobe part 14.1 rolling over the underlying surface causes the lobe 14 to pivot about the pivot 16. When the lobes have reached their new positions the rams 15 are hydraulically locked to maintain the lobes 14 in their new positions.

Alternatively, springs (not shown) may be provided to bias the portions 14.1 of the lobes 14 towards the centre of gravity 17. Upon release of the locking means, the lobe portions 14.1 are pulled towards the centre of gravity 17 by the springs. The roller can therefore be adjusted from a non-circular profile to a circular profile during operation of the roller.

In an alternative manner of changing the profile from that shown in FIG. 2- to that shown in FIG. 1, the locking means, i.e., hydraulic rams 15 are released while the roller continues to rotate in the direction of arrow 20. During this movement the lobe part 14.2 rolling over the underlying surface causes the lobe 14 to pivot about the pivot 16. The hydraulic rams 15 are hydraulically locked to lock the lobes 14 in position as soon as their new positions are reached.

In the position shown in FIG. 1, Le, when the profile is circular, the roller delivers no impact and it can travel from one'site to another and over vulnerable structures, such as bridges, where no impact has to be delivered. b

In the position shown in FIG. 2, i.e., when the profile is non-circular, the centre of gravity 17 has a lift R-r and the roller delivers impact when travelling over a surface.

Referring to FIG. 3, there is shown diagrammatically an alternative arrangement 22 for deforming the crosssectional profile of the roller 10 shown in FIG. 1. The arrangement 22 permits the profile to be deformed mechanically and comprises a screw-threaded shank 24 pivotally connected at 26 to the part 14.1'of each lobe 14. A screw-threaded gear 28 co-operates with the shank 24 and is axially restrained between guides 30 and 32. The guides 30 and 32 are interconnected with each other and are pivotally mounted at 34 on the roller core 12. A drive gear 36 which is driven electrically. hydraulically or mechanically is provided to drive the gear 28. When the gear 28 is rotated, the shank 24 is axially displaced, whereby each lobe 14 is pivoted about its pivot 16.

The roller 10 has an axle 38 which may be a driven axle fast with the roller core 12 so that traction is trans mitted via the roller itself, in other words, the roller is self-propelled in this arrangement. This may for instance be effected by co-ordinated and cyclic displacement of the hydraulic rams 15. Alternatively, the roller may have a drawbar similar to the drawbar 44 shown in FIG. 5.

The locking means, i.e., hydraulic cylinders 13 and rams 15, may be arranged to permit a plurality of lobe settings between a circular profile as shown in FIG. I when no impact is delivered and a non-circular profile as shown in FIG. 2 when maximum impact is delivered. The particular lobe setting is selected to produce a particular lift for the centre of gravity for achieving a particular depth and degree of compaction in an underlying layer of soil or gravel.

FIG. 4 shows an alternative embodiment 37 of an impact roller basically the same as the embodiment of FIG. I except that the lobes 39 have a flatter curve, i.e., a larger radius than the lobes 14 of embodiment 10. The centre of curvature of each lobe 39 in roller 37 never coincides with the centre of gravity 17 of the roller, whereas in the roller 10 when adjusted to the profile shown in FIG. 1, the centre of curvature of each lobe 14 coincides with the centre of gravity 17 of the roller. The cross-sectional profile of the roller 37 is deformed in exactly the same manner as the crosssectional profile of roller 10, i.e., by employing rams which are pivotally attached to the lobes at 15.1 and to the roller core 12 at 13.1. The only constructional difference is that the cross-sectional profile of roller 37 cannot be adjusted to a fully circular shape like the cross'sectional profile of roller 10. The advantage of roller 37 over roller 10 is that'when roller 37 is adjusted to have a non-circular profile similar to the profile of roller 10 shown in FIG. 2, the projecting regions on the lobes 39 of roller 37 dig into the underlying soil to a lesser extent than the corresponding regions 14.2 of the lobes 14 of roller 10 when operating in noncohesive soils.

In an additional or alternative construction for adjusting the cross-sectional profiles of the rollers 10 and 37 of FIGS. 1 and 4, the pivots 16 of the lobes 14 and 39 may be displaceable towards or away from the centre of gravity 17. The pivots 16 may be displaceable by hydraulic rams similar to the rams 15.

Referring to FIGS. 5 and 6, there is shown another embodiment of an impact roller having a deformable cross-sectional profile. The roller 40 comprises an axle 42 to which is attached a drawbar 44 via bearings 46. On the axle 42 is mounted a wheel 48 such as a rim of motor vehicle wheel. Between the axle 42 and the wheel 48 is provided a bearing 50 to facilitate rotation of the wheel about the axle.

On the wheel 48 is mounted an annular elastic bag 52 such as a pneumatic tyre of a motor vehicle wheel. An annular chamber 54 is defined between the wheel 48 and the bag 52. The gas pressure in the chamber 54 can be varied, even when the roller 40 is in operation. The means for varying the gas pressure is not shown, but it may include a gas reservoir, a compressor for supplying compressed gas such as air to the reservoir, pneumatic lines between the chamber 54 and the reservoir, and a valve arrangement in the pneumatic lines to control gas flow in the lines. A pressure gauge (not shown) is also provided to indicate the gas pressure in the chamber 54.

The elastic bag 52 and wheel 48 are enclosed in a cage comprising two cheek plates 56 and a plurality of lobes 58 pivotally mounted on pivot pins 60 between the cheek plates 56. The external periphery of the annular bag 52 abuts the inwardly disposed surfaces of the lobes 58. A central aperture 62 is provided in each cheek plate 56 so that the cheek plates 56 fit with clearance around the axle 42 to permit relative radial movement between the axle and the cheek plates. It will be seen from FIGS. 5 and 6 that the lobes 58 form the periphery of the roller 40. The cross-sectional profile of the roller is deformed during travel of the roller over a surface since the lobes 58 pivot about the pivot pins 60 and press into the periphery of the bag 52 as shown in FIG. 7. The degree of deformation is inversely proportional to the gas pressure in the bag 52, Le, the higher the pressure the less deformation is permitted and vice versa.

Referring further to FIG. 5, the roller is shown as having a circular cross-sectional profile. In this condition the gas pressure in the chamber 54 is high so that the pneumatic bag 52 is pressed tightly against the lobes 58, thus permitting no or a negligible deformation of the bag 52 and consequently little or a negligible piv otting of the lobes 58 about the pivot pins 60. The centre of gravity 64 of the roller has a zero or a negligible lift in this condition so that no impact or a negligible impact is delivered to the underlying surface 66.

The lobes 58 shown in FIGS. 5 and 6 are of circular arcuate shape, but the lobes may have flat surfaces, for example by being flat panels. The roller 40 may be selfpropelled by controlled and synchronised actuation about the axle 42.

Referring to FIG. 7, the roller 40 is shown with maximum deformation of its cross-sectional profile. In this condition the gas pressure in the chamber 54 is low so that during travel of the roller over the surface 66, the lobes 58 are permitted to deform the bag 52 as shown and to pivot about the pivot pins 60. The centre of gravity 64 in this condition has a lift R-r so that impact is delivered to the underlying surface 66 during travel of the roller over the surface.

Referring to FIGS. 8 and 9, there are shown fragmentary side and sectional views of a roller 40.l similar to the views of roller 40 shown in FIGS. 5 and 6. The parts shown in FIGS. 8 and 9 are identical to the parts shown in FIGS. 5 and 6 except that the construction of the lobes 58.1 in FIGS. 8 and 9 is-different from the construction of the lobes 58 in-FIGS. Sand 6. The lobe 58.1 has an inwardly projecting formation 58.2 which is slightly smaller in width than the lobe 581. The overall thickness of the lobe 58.1 including the formation 58.2 is larger than the thickness of the lobe parts 58.3 and 58.4. The object of the formation 58.2 is to effect deformation of the bag 52 opposite the pivot 60. Such deformation is advantageous in providing resilience between the drawbar 44 and the axle 42 and such resilience is advantageous in dampering relative horizontal movement between the drawbar 44 and the axle 42. Relative horizontal movement between the drawbar and the axle is caused by the inertia of the roller when the roller profile is deformed so that the centre of gravity has a lift R-r as in FIG. 7. Such relative horizontal movement is permitted by the apertures 62 in the I cheek plates 56.

The pivots 60 of the lobes 58 and 58.1 of FIGS. and 8 are shown symmetrically positioned on the lobes, but if desired, the pivots may be asymmetrical.

In order to produce a particular lift for the centre of gravity 64 for delivering a desired impact in particular soil or gravel conditions, a particular gas pressure in the chamber 54 is selected.

The drawings only show specific examples of means to effect deformation of the cross-sectional profiles of the rollers 10. and 40. Other means may be used such as a cam and follower arrangement, and electric solenoids to effect the deformation electromagnetically.

One advantage of an impact roller in accordance with the invention is that a specified density in a material can be achieved economically by selecting an appropriate lift for the centre of gravity. The energy delivered per blow during rotation of the roller is dependent on the lift. The greater the energy, the greater the depth to which compaction will be effective. However,

a great depth is not always required. It is then economi- I cal to set the lift to achieve only the specified density, i.e., a lesser lift is selected.

An additional advantage arising from the advantage mentioned in the preceding paragraph is that a higher operating speed is possible with a lower lift, thereby achieving a still further economy.

A further advantage is that in too soft, rough and uneven terrain the roller profile can be set circular for preparing the surface initially and thereafter the roller profile is set non-circular for impact compaction.

A still further advantage of an impact roller according to the invention is that its profile can be adjusted to a circular shape to facilitate its movement over or near vulnerable structures while in operation.

I claim:

1. An impact roller which includes a core structure; a plurality of axially extending lobes forming the periphery of the rollers and defining its cross-sectional profile, the lobes being circumferentially spaced about the core structure and each lobe subtending a minimum angle of approximately between radii and having a lifting surface and a tamping surface and being mounted to pivot on the core structure about an axis parallel to the roller rotational axis, the said pivotal axis being disposed between the lifting and tamping surfaces, and the disposition of each lobe being adjustable about its pivotal axis relative to the core structure such that the distance of the lifting surface from the rotational axis of the roller is greater than the distance of the tamping surface from'the rotational axis of the roller thereby effecting the cyclic lifting of the centre of gravity of the roller during rotation of the roller over a surface; and adjusting means interconnecting the core structure and the lobes for adjusting the pivotal dispositions of the lobes about their pivotal axes relative to the core structure thereby to adjust the relative positions of the lifting surfaces and the tamping surfaces of the lobes and to vary the degree of cyclic lift of the center of gravity of the roller during operation.

2. An impact roller which includes a core structure; a plurality of axially extending lobes forming the periphery of the roller and defining its cross-sectional profile, the lobes being circumferentially spaced about the core structure and each being mounted to pivot on the core structure about an axis parallel to the roller rotational axis, and. fluid pressure means to deform the cross-sectional profile of the roller by causing the lobes to pivot about their pivotal axes to vary the lift of the centre of gravity of the roller when it rolls, the fluid pressure means including a fluid pressure ram attached to each lobe to displace the lobe relative to the other lobes and the core structure and to maintain the lobe in any desired position about its pivotal axis relative to the other lobes and to the core structure.

3. An impact roller which includes a core structure; a plurality of axially extending lobes forming the periphery of the roller and defining its cross-sectional profile, the lobes being circumferentially spaced about the core structure and each being mounted to pivot on the core structure about an axis parallel to the roller rotational axis; and fluid pressure means for deforming the cross-sectional profile of the roller to vary the lift of the centre of gravity of the roller, the fluid pressure means including an elastic bag adapted to hold a fluid under pressure and arranged radially inwardly of the lobes, the bag, when pressurized, abutting the lobes and permitting pivotal displacement of the lobes about their pivotal axes and thereby deformation of the crosssectional profile of the roller when it rolls along a surface, the degree of displacement of the lobes and thus the degree of deformation of the profile being inversely proportional to the fluid pressure in the bag.

4. An impact roller which includes a core structure; a plurality of axially extending lobes forming part ofthe periphery of the roller, the lobes being circumferentially spaced about the core structure and subtending a minimum angle of approximately 30 between radii, and each lobe having a lifting surface, and being mounted to pivot on the core structure about an axis parallel to the roller rotational axis, the disposition of each lobe being adjustable about its pivotal axis relative to the core structure whereby the distance of the lifting surface from the rotational axis of the roller is adjustable between a setting in which there is no cyclic lifting of the centre of gravity of the roller during operation when it rolls along a surface, and a maximum setting when there is maximum cyclic lifting of the centre of gravity of the roller during operation.

5. An impact roller which includes a core structure; a plurality of axially extending lobes forming the periphery of the roller and defining its cross-sectional profile, the lobes being circumferentially spaced about the core structure and each lobe having a lifting surface and a tamping surface and being mounted to pivot on the core structure about an axis parallel to the roller rotational axis, the said pivotal axis being disposed between the lifting and tamping surfaces, and the disposition of each lobe being adjustable about its pivotal axis relative to the core structure such that the distance of the lifting surfacefrom the rotational axis of the roller is greater than the distance of the tamping surface from the rotational axis of the roller thereby effecting the cyclic lifting of the centre of gravity of the roller during rotation of the roller over a surface; and adjusting means interconnecting the core structure and the lobes for adjusting the pivotal dispositions of the lobes about their pivotal axes relative to the core structure, thereby to adjust the relative positions of the lifting surfaces and the tamping surfaces of the lobes and to vary the degree of cyclic lift of the centre of gravity of the roller during operation, the adjusting means including a screw-threaded shank connected at one end to a lobe away from its pivotal axis, and a nut held captive on the core structure and cooperating with the shank for varying the effective length ofthe shank between the lobe and the core structure. 

1. An impact roller which includes a core structure; a plurality of axially extending lobes forming the periphery of the rollers and defining its cross-sectional profile, the lobes being circumferentially spaced about the core structure and each lobe subtending a minimum angle of approximately 30* between radii and having a lifting surface and a tamping surface and being mounted to pivot on the core structure about an axis parallel to the roller rotational axis, the said pivotal axis being disposed between the lifting and tamping surfaces, and the disposition of each lobe being adjustable about its pivotal axis relative to the core structure such that the distance of the lifting Surface from the rotational axis of the roller is greater than the distance of the tamping surface from the rotational axis of the roller thereby effecting the cyclic lifting of the centre of gravity of the roller during rotation of the roller over a surface; and adjusting means interconnecting the core structure and the lobes for adjusting the pivotal dispositions of the lobes about their pivotal axes relative to the core structure thereby to adjust the relative positions of the lifting surfaces and the tamping surfaces of the lobes and to vary the degree of cyclic lift of the center of gravity of the roller during operation.
 2. An impact roller which includes a core structure; a plurality of axially extending lobes forming the periphery of the roller and defining its cross-sectional profile, the lobes being circumferentially spaced about the core structure and each being mounted to pivot on the core structure about an axis parallel to the roller rotational axis, and fluid pressure means to deform the cross-sectional profile of the roller by causing the lobes to pivot about their pivotal axes to vary the lift of the centre of gravity of the roller when it rolls, the fluid pressure means including a fluid pressure ram attached to each lobe to displace the lobe relative to the other lobes and the core structure and to maintain the lobe in any desired position about its pivotal axis relative to the other lobes and to the core structure.
 3. An impact roller which includes a core structure; a plurality of axially extending lobes forming the periphery of the roller and defining its cross-sectional profile, the lobes being circumferentially spaced about the core structure and each being mounted to pivot on the core structure about an axis parallel to the roller rotational axis; and fluid pressure means for deforming the cross-sectional profile of the roller to vary the lift of the centre of gravity of the roller, the fluid pressure means including an elastic bag adapted to hold a fluid under pressure and arranged radially inwardly of the lobes, the bag, when pressurized, abutting the lobes and permitting pivotal displacement of the lobes about their pivotal axes and thereby deformation of the cross-sectional profile of the roller when it rolls along a surface, the degree of displacement of the lobes and thus the degree of deformation of the profile being inversely proportional to the fluid pressure in the bag.
 4. An impact roller which includes a core structure; a plurality of axially extending lobes forming part of the periphery of the roller, the lobes being circumferentially spaced about the core structure and subtending a minimum angle of approximately 30* between radii, and each lobe having a lifting surface, and being mounted to pivot on the core structure about an axis parallel to the roller rotational axis, the disposition of each lobe being adjustable about its pivotal axis relative to the core structure whereby the distance of the lifting surface from the rotational axis of the roller is adjustable between a setting in which there is no cyclic lifting of the centre of gravity of the roller during operation when it rolls along a surface, and a maximum setting when there is maximum cyclic lifting of the centre of gravity of the roller during operation.
 5. An impact roller which includes a core structure; a plurality of axially extending lobes forming the periphery of the roller and defining its cross-sectional profile, the lobes being circumferentially spaced about the core structure and each lobe having a lifting surface and a tamping surface and being mounted to pivot on the core structure about an axis parallel to the roller rotational axis, the said pivotal axis being disposed between the lifting and tamping surfaces, and the disposition of each lobe being adjustable about its pivotal axis relative to the core structure such that the distance of the lifting surface from the rotational axis of the roller is greater than the distance of the tamping surface from the rotational axis of the roller thereby effecting the cyclic lifting of the centre of gravity of the roller during rotation of the roller over a surface; and adjusting means interconnecting the core structure and the lobes for adjusting the pivotal dispositions of the lobes about their pivotal axes relative to the core structure, thereby to adjust the relative positions of the lifting surfaces and the tamping surfaces of the lobes and to vary the degree of cyclic lift of the centre of gravity of the roller during operation, the adjusting means including a screw-threaded shank connected at one end to a lobe away from its pivotal axis, and a nut held captive on the core structure and cooperating with the shank for varying the effective length of the shank between the lobe and the core structure. 